Re: How to sample multiple signals at the same time with ADC?

Mike Noone wrote:
Hi - I'm working on a project where I'm going to have 12 different
channels of data that I will be sampling at about 2KHz. I need I think
about 16 bits of accuracy, maybe a little less. I would really like to
take all these samples at *exactly* the same time. So - I could have 12
ADCs on the board... But that'd be just a tad spendy, to say the least.
What I don't care too much about is how long it takes to digitize each
signal, as long as all are digitized in under half a milisecond (1/2K
seconds). So ideally I'd like a chip that could sample and hold all the
signals at the same time, and then go back and individually digitize
them. Are there any ADCs that can do this for me? If not - are there
any good solutions to this problem? I should mention that I might end
up needing only 4 channels, not 12. (I'll have 3 boards with 4 channels
each - but I'm not sure if I want an ADC on each board or just one ADC
for all 3).

Other details if they matter - the devices being samples will be an
Analog Devices accelerometer and an Analog Devices gyro as well as
probably a Honeywell magnetometer. Fourth channel is the temperature
sensor on the gyro.

Thanks!

-Mike

You could use a multiplexed A-D and front end sample hold ICs - it's
possible to make your own, of course, but unless you are trying to
squeeze the last cent from the design or some other special reason, I'd
go with a premade one.

16 bits of resolution implies 0.001% accuracy for all errors. Even the
best ICs I could find (Analog devices) spec 14 bit accuracy (and are
expensive - $9 - $34 each depending on which one you choose).
http://www.analog.com/en/subCat/0,2879,773%255F925%255F0%255F%255F0%255F,00.html

Much cheaper is the LF398 (298/198) [A] range from National
http://www.national.com/pf/LF/LF398.html

Has 0.002% gain accuracy, [15 bit accuracy without including other
errors], so droop will be the major limiting factor.

You could probably get 12 bits [enob] out of this without much trouble.

Cheers

PeteS

.

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